A wind turbine known in the art comprises a wind turbine tower and a wind turbine nacelle positioned on top of the tower. A wind turbine rotor with a number of wind turbine blades is connected to the nacelle through a low speed shaft, as illustrated on FIG. 1.
Somewhere between the nacelle and the rotor the wind turbine is typically provided with a main bearing unit to ensure substantially frictionless rotation of the rotor in relation to the nacelle while transferring the load or loads from the rotor to the nacelle.
Previously at this main bearing unit, often one or more relatively small bearings enclose a solid or at least a very thick-walled low speed shaft, but as wind turbines have grown bigger and bigger both in output and in size, the trend today is more towards large diameter main bearing units e.g. enclosing the gearbox as disclosed in U.S. Pat. No. 6,232,673 B1.
For such a main bearing unit to be efficient it has to be very rigid or at least rigidly mounted on very rigid parts of the hub and/or the nacelle and the more load the bearing unit has to transfer or the bigger diameter the main bearing unit has, the more costly it is to obtain satisfactory rigidity.
An object of the invention is to provide for a method and a wind turbine comprising a main bearing unit, which is advantageous for the operation of large modern wind turbines.